1. Field of the Invention
The present invention relates generally to an automotive cabin heating arrangement and more specifically to a heating arrangement which is incorporated with an evaporative type engine cooling system wherein the coolant is permitted to boil and the vapor used as a vehicle for removing heating from the engine, which minimizes the time after a cold engine start that cabin heating may be realized and which maximizes the amount of heat for the given heater which can be released into the cabin after the engine is fully warmed up.
2. Description of the Prior Art
FIG. 1 of the drawings shows a conventional cabin heating arrangement which is incorporated with a coolant circulation type engine cooling system. With this type of arrangement as the amount of coolant contained in the cooling system is inherently large, a relatively long period is required from the time the engine undergoes a "cold" start and the time which heated coolant is available for cabin heating purposes.
A further drawback encountered with this system is that the load on the coolant circulation pump is increased by the relatively long lengths of conduiting required to lead the heated coolant from the engine to the core of the cabin heater and back again to the coolant jacket of the engine. For example, given that the temperature difference between the inlet and discharge ports of the coolant jacket is 4.degree. C., the amount of heat which 1 Kgm of water (coolant) can remove from the engine is 4 Kcal. Accordingly, in the case of an engine having a 1800 cc displacement (by way of example) the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this, a flow rate of 167 Liter/min must be produced by the coolant circulation pump. This of course consumes a number horse power. The addition of the cabin heating circuit circulation to the normal coolant circulation load only increases the amount of power which is consumed by the parasitic pump and which therefore cannot be supplied to driving wheels of the vehicle.
FIG. 2 shows an arrangement which is disclosed in U.S. Pat. No. 2,413,770 issued in Jan. 7, 1947 in the name of M. F. Knoy and which has sought to overcome the various drawbacks inherent in coolant circulation type cooling systems. In this arrangement the coolant is permitted to boil and the vapor used a vehicle for removing heating from the engine. This eliminates the need for a power consuming circulation pump. Moreover, the vapor can be supplied to a condenser (heater core) disposed in the passenger compartment of the vehicle in a manner to make use of the powerful heating effect possible by utilizing the latent heat of evaporation contained in the coolant vapor.
However, this type of arrangement has suffered from two major drawbacks. Firstly, the cabin heating system is not enabled until the engine has warmed sufficiently (after a cold start) to induce the coolant to boil and coolant vapor made available for cabin heating purposes and secondly, with the passing of time air tends to contaminate the system and badly impair the heat exchange efficiency of both of the engine radiator and the cabin heating arrangement. Viz., when the engine is stopped and the coolant vapor condenses, as the coolant jacket is only partially filled with liquid coolant a negative pressure tends to be produced which inevitably causes atmospheric air to leak in and contaminate the system. Upon restart of the engine the non-condensible matter (air) tends to be carried toward and into the radiator and cabin heater core by the coolant vapor. However, due to the tendancy for hot air to rise and the tendancy for condensed coolant to descend, a kind of embolism develops in the heat exchanging devices which drastically reduces the surface area available for heat exchange and thus badly impairs the efficiency of same.
FIG. 3 of the drawings shows a more recently proposed arrangement which is disclosed in U.S. Pat. No. 4,367,699 issued in Jan. 11, 1983 in the name of Evans. This arrangement while being a little more elaborate than the arangement shown in FIG. 2 tends to suffer from essentially the same demerits. That is to say, upon engine shut-down and the inevitable condensing of the coolant vapor, the resulting negative pressure which develops within the system is sufficient to suck air thereinto through a pressure relief valve arrangement A. It should be noted that this valve arrangement is such as to open to permit excess pressure to be vented from the system (for example upon a positive pressure of 0.2 to 1.0 Atmos. developing) and to permit the entry of air upon a negative pressure of approximately 0.34 Atmos. prevailing in the system.
A further drawback encountered with this system comes in the need for the gravity feed tank-like arrangement B which permits separation of liquid and gaseous coolant before the gaseous coolant is conducted to the condenser C and to the cabin heater core D. This arrangement render the system both bulky and difficult to dispose within the very limited space available within the engine compartment of modern automotive vehicles.